A duty ratio under different working conditions is determined according to an analysis of a characteristic parameter x of a motor of a power tool and then a drive circuit is controlled with the duty ratio to drive the motor to operate. It is only needed to calculate the duty ratio without needing to make any variable to the circuit hardware or the mechanical structure of the power tool. That is, the duty ratio can be adjusted to achieve optimized control of the motor, thereby optimizing the working performance such as an output torque of the power tool.